"Physical preparation: should stretching be included
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By
Adam Sayers, Ph.D, Middle Tennessee State University
Jennifer Caputo, Ph.D, Middle Tennessee State University
John Ferguson, DA, Eastern Kentucky University
Colby B. Jubenville, Ph.D, Middle Tennessee State University |
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The articles of our authors are indexed in |
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The value of static stretching prior to physical activity has been known to yield positive results for many years. Some of the perceived benefits include reduced injury and improved performance correct? Well, let's consider some of the recent research in this area and decide if we are helping or hindering participants in physical activity by encouraging the use of various types of static stretches!
Static stretching can be defined as the slow, gradual lengthening of a muscle to an elongated position, and the holding of that position for 10 to 30 seconds (Donatelle, 2003). Static stretching prior to participation in athletic activity is common across all levels of sports, both competitive and recreational. It is recommended by coaches, trainers, physiotherapists, and physicians in an effort to both prevent injury and enhance performance. However, the practice of pre-performance stretching has largely been based on intuition and unsystematic observation rather than on scientific evidence (Thacker, Gilchrist, Stroup, & Kimsey, 2004).
Early research concerning the effects of static stretching produced inconclusive results. For example, Moeller, Ekstrand, Oberg, and Gillquist (1985) found that static stretching can temporarily increase range of motion for up to 90 minutes, thereby benefiting participants in such activities as gymnastics and dancing. However, Rosenbaum and Hennig (1995) found that static stretching can cause a 5% to 25% decrease in strength. Despite conflicting results, the notion that benefits can be achieved from static stretching prior to activity is still valued.
There are several explanations for the inconsistent nature of these results including lack of controls and questionable methodologies. Thacker et al. (2004) noted that in many studies, several potential risk factors such as fitness levels and extremes in body mass index were not addressed, and potential confounding variables were ignored. Thacker et al. also identified several measurement and methodological deficiencies in past studies, including ascertainment and information biases and a lack of sufficient statistical power. |
| 2. Static Stretch Risk of Injury? |
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Pope et al. (2000) studied the effects of static stretching on injury risk. They randomly allocated 1,538 male army recruits to static stretch and control groups. Participants in the stretch group statically stretched several lower-limb muscle groups (e.g., gastrocnemius, soleus, hamstrings, quadriceps, hip adductors, and hip flexors) every other day for 20 seconds each prior to training. Training consisted of 40 training sessions during 11 weeks, totaling 50 hours of exercise. Stretch group members interspersed four minutes of light jogging and side-stepping with their stretching routines. Control group participants engaged in the warm-up jogging without static stretching. During the course of training, there were 175 lower-limb injuries in the control group compared to 158 in the stretch group. Although the total number of injuries was slightly higher in the control group, the difference between the groups was not statistically significant. While the results cannot be generalized to competitive sport, these results provide evidence that static stretching prior to physical activity does not reduce the risk of injury.
The relationship between static stretching and injury risk was also explored by Dadebo et al. (2004). The researchers conducted a survey of training protocols and hamstring strains in professional soccer clubs in England across four professional divisions. It was found that the higher-ranked clubs performed the most static stretching, and that these clubs also had the highest hamstring strain rates, as compared to lower-ranked clubs. However, these data do not indicate a direct relationship between pre-exercise stretching and hamstring injury rate, nor was the intensity of play controlled.
Herbert and Gabriel (2002), in a systematic review of the literature on the effects of static stretching on injury risk and muscle soreness, offered several theories as to why pre-performance stretching does not decrease the risk of injury. Notably, they stated that most injuries occur during eccentric contractions within the normal range of joint motion. Therefore, given that stretching increases joint range of motion, injuries occurring during eccentric contractions within the normal range of joint motion will not be affected by pre-performance stretching. |
| 3. Static Stretch Improved Performance? |
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Herbert and Gabriel (2002) concluded that insufficient research exists on the effects of pre-exercise static stretching on performance. However, some data illustrate that static stretching prior to physical activity can have a negative effect on performance. Additionally, several studies published subsequent to Herbert and Gabriel's review have produced results that negate the widely-held notions of the benefits of static stretching, notably maximal strength performance.
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| 4. Maximal Strength & Static Stretching |
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The negative relationship between static stretching and maximal strength performance has been found by several researchers (Boyle, 2004; Cramer et al., 2005; Cramer et al., 2004; Kokkonen et al., 1998). Kokkonen et al. found that statically stretching the knee flexors and the knee extensors caused a significant decrease in knee-flexion 1RM. They conjectured that the post-stretching strength deficit could be the result of a reduction in either passive or active stiffness of the musculotendinous unit, a relationship suggested in previous work by Magnusson, Simonsen, Aagaard, and Kjaer (1996) and Rosenbaum and Henig (1995). Kokkonen et al. concluded that, in any event in which success is dependent upon maximal strength output, static stretching of the prime-movers used in the activity should not be undertaken prior to participation.
These results are supported by the more recent findings of Cramer et al. (2004). Cramer et al. investigated the effects of static stretching on concentric, isokinetic leg extension peak torque in stretched and unstretched limbs. After measuring peak torque in both limbs at 60°·s -1 and 240°·s -1 , t he participants performed one active stretch and three passive stretches of the leg extensors in the dominant limb. Peak torque was then reassessed. It was found that peak torque decreased after static stretching in both limbs and at both velocities. The researchers suggested that the decrease could have been caused by changes in the mechanical properties of the muscle that may have affected the muscle's length-tension relationship. Alternatively, they suggested that the detriment could be attributed to neural factors such as a CNS inhibitory mechanism that possibly affected muscle activation or reflex sensitivity. The fact that both limbs (stretched and unstretched) showed a decrease suggests the latter. A limitation in this particular study arises due to the dual administration of active and passive stretching. The aforementioned stretching techniques produce a vastly different intensity of stretch, therefore resulting in a lack of control in the administration of the stretching intervention. It is clear that the intensity of the stretch should be controlled in order to produce more valid results.
These findings were further substantiated in 2005 by Cramer et al. Peak torque in the dominant and nondominant limbs was assessed at 60°·s -1 and 240°·s -1 both before and after four stretches (one active and three passive) of the leg extensors in the dominant leg. A decrease in peak torque was found in the dominant leg at both velocities and in the nondominant leg at 60°·s -1 . The researchers concluded that the decreases in peak torque could be caused by a CNS inhibitory mechanism because the deficit occurred in both limbs.
Boyle (2004) investigated the effects on muscle force production of warm-up protocols featuring a static or a dynamic stretching regimen. Prior to each warm-up regimen, the participants were assessed for concentric and eccentric quadriceps peak torque. On each of four consecutive days, the participants were randomly assigned to one of four different stretching routines, summarized by the researcher as: no stretch (15-minute rest), static-15 (five static stretches of the quadriceps, 3 x 15 s; 20 s recovery), static-30 (five static stretches, 3 x 30 s; 20 s recovery) and dynamic (five dynamic stretches, 5 x 8 repetitions; 20 s recovery). The stretching routines were preceded by 10-minutes of jogging on a treadmill. Following the stretching regimens, the participant's muscle force production (concentric and eccentric) in the quadriceps was measured.
Significant differences were found for both concentric peak torque and eccentric peak torque. The researcher also discovered that, when compared with the no stretch condition, participants experienced lower concentric peak torque values for the static-30 condition and higher values for the dynamic condition. Participants also had higher values in eccentric peak torques for the dynamic condition, and lower values for both the static-15 and static-30 condition, compared with the no stretch condition. Boyle (2004) found that, when compared to a warm-up that does not involve stretching, static stretching during a warm-up significantly reduced both concentric and eccentric peak torque of the quadriceps, whereas dynamic stretching led to improvements in muscle force production. These results indicate both the negative effects of static stretching and the benefits of a dynamic warm-up routine prior to activity. Boyle (2004) concluded that caution should be exhibited when planning or prescribing a warm-up routine prior to physical activity, particularly activity that requires optimal muscle performance, and recommended that future research should focus on the provision of dynamic alternatives that mimic sport-specific movements. The results of studies investigating the effects of static stretching on maximal strength performance are consistent with those using explosive force production as a dependent variable. |
5. Explosive Force Production Improved? |
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The effects of static stretching on explosive force production of the muscle have been explored to a certain extent, all yielding similar results indicating that static stretching may have a negative influence on performance (Siatras, Papadopoulos, Mameletzi, Gerodimos & Kellis, 2003; Young & Behm, 2003; Young & Elliott, 2001). Young and Elliott explored the effects of static stretching on jumping performance and explosive force production. The study involved 14 participants who completed four different warm-up conditions, performed on different days, 2-4 days apart. Each session involved a 5-minute jog followed by one of the conditions, including static stretching. After a 4-minute rest period, the participants performed two vertical jumping tests, a squat jump and a drop jump, to determine lower body explosive force production and jumping performance. The researchers reported that static stretching prior to performance produced a decrement in drop jump, consisting of jumping from a 30-cm high box onto a mat, measured in height/time performance, and a decrease in concentric explosive muscle performance. Young and Elliott reiterated that different forms of muscle functions are performed by the body in varying capacities across different sports. Therefore, the differences in warm-ups and other preparation techniques needed to obtain maximum performance in each sport should be investigated.
Young and Behm (2003) compared the effects of running, static stretching, and practice jumps on explosive force production and jumping performance. Male ( n = 13) and female ( n = 3) volunteers participated in five different warm-ups, including control, 4-minute run, static stretch, run and stretch, and run, stretch, and practice jumps in counterbalanced order before performing two jumping tests. The jumping tests, a concentric jump and drop jump, were performed following a 2-minute rest interval after the warm-up. The researchers identified six dependent variables including concentric jump height, peak force, rate of force developed, drop jump height, contact time, and height/time to measure fast force production and jumping performance. The results indicated that the run, stretch, and jumps warm-up produced the highest values, and the static stretch warm-up produced the lowest values of explosive force production. The run warm-up produced statistically better performance than the run and stretch warm-up. The researchers concluded that practice jumps and running positively affect performance, whereas static stretching negatively affects performance. These results suggest that static stretching can also effect performance of an activity that relies on rate of force production or power, not just maximal force output.
Siatras et al. (2003) investigated the effect of static and dynamic acute stretching on gymnasts' speed in vaulting. On three non-consecutive days, the participants performed three different preparation protocols including warm-up, warm-up and static stretching, and warm-up and dynamic stretching. A handspring vault followed each protocol. There was a statistically significant difference in gymnasts' speed following each of the different protocols. The static stretching protocol produced a significant decrease in gymnasts' speed. The researchers concluded that acute static stretching prior to performance had a detrimental effect on the gymnasts' running speed. One implication of this study is that athletes and coaches should re-evaluate their preparation techniques in order to maximize performance in their specific sport. The need for further research into the effects of including static stretching in sport-specific warm-up routines on athletic performance is evident. Given the evidence indicating a detrimental effect of static stretching, it has been recommended that the relationship between static stretching and perceived exertion be investigated. |
6. Perceived Exertion & Muscle Fatigue |
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Laur, Anderson, Geddes, Crandall, and Pincivero (2003) explored the effects of acute stretching on hamstring muscle fatigue and perceived exertion. Participants were randomly assigned to a control group and a treatment (static stretch) group. After the warm-up, the participants were asked to perform as many hamstring curls at 60% of their one repetition maximum as possible. The participants returned within one week to complete the experiment, at which time the treatment was administered to the control group. The researchers found that, when compared to the stretch condition, participants in the non-stretch condition exhibited significantly higher power function exponents. Also, the treatment group had a significantly higher first repetition rating of perceived exertion than the control group. The researchers concluded that their findings reflected the results of other recent studies in which acute static stretching was found to inhibit muscle force production. They also stated that this pattern was reflected in ratings of perceived exertion. Laur et al. recommend that future research should investigate the functional significance of the effects of static stretching on muscle performance. Even though studies exploring the effects of static stretching on various aspects of muscle performance are becoming more prevalent, an area that has been largely ignored is that of sprint performance. |
An activity common to many sports is sprinting. Nelson et al. (2005) investigated the effects of passive muscle stretching on sprint performance. The participants included 11 males and 5 females from a nationally ranked Division I university track and field team. Nelson et al. used four different stretching protocols: No stretch in either leg (NS), both legs stretched (BS), forward leg in the starting position stretched (FS), and rear leg in the starting position stretched (RS). The participants were randomly assigned to the stretching groups. Prior to being stretched, the participants performed an identical light mobility warm-up, and no other activity was allowed other than the stretching. The stretching protocols included static stretches designed to stretch the calf, quadriceps, and hamstring muscles. For each stretch, the range of motion was increased until the participant felt a slight degree of discomfort, and was held for 30 seconds. The participants had a 10 second - 20 second rest between each stretch. After a full cycle (each stretch performed once), the participants had an additional 20 second - 30 second rest and repeated the cycle four times. After the stretching regime was completed, the athletes relaxed for 5 minutes 10 minutes before the sprinting began. Each athlete performed three 20-meter sprints, with a 1-minute recovery after each sprint.
No significant difference was found among the three stretch conditions (BS, FS, RS), however, the times for the three stretch conditions were all statistically slower than the no-stretch condition. An additional analysis on the best time for each trial, as opposed to the average, yielded similar results. It was concluded that pre-performance stretching negatively impacted 20-meter sprint performance.
Nelson et al. (2005) offered several suggestions as to the mechanisms that could have potentially caused the detriment in sprint performance. They conjectured that static stretching may have reduced the stiffness of the musculotendinous unit. A stiffer musculotendinous unit improves force production, allowing greater length and reduced shortening velocity of the contractile component. Therefore, the muscle is at a more advantageous point on both the force-velocity and force-length curve. However, through the use of static stretching, stiffness of the musculotendinous unit is reduced, ultimately preventing the quadriceps and hamstrings from operating at the most advantageous part of the force-length and force-velocity curves, therefore hampering sprint performance. Alternatively, it was suggested that the stretching had an effect on the stretch-shortening cycle, causing an increase in musculotendinous compliance. This reduces the ability of the muscle to store and reuse elastic energy, which decreases force production. In addition to the possibility of these mechanical mechanisms being affected by static stretching, the researchers also suggested that the performance decrease could be associated with neurological mechanisms. One such proposition suggests that stretching could reduce stretch reflex strength, which is again related to the stretch-shortening cycle. During the eccentric phase of a stretch-shortening cycle, a myoelectric potentiation (stretch reflex) is initiated, which increases muscle activation during the concentric phase. It was suggested that stretching can reduce this myoelectric potentiation, thereby negatively effecting sprint performance, as reported earlier by Rosenbaum and Hennig (1995).
Additionally, Nelson et al. (2005) also found that the same detrimental effects were experienced whether the athletes stretched both legs or just one leg. Thus, stretching one leg appears to be sufficient for adversely affecting performance. However, given the nature of the participants and the conditions in which they were performing the activity, these results cannot be generalized to other sports.
Fletcher and Jones (2004) yielded similar results when investigating the effects of different warm-up protocols on 20-meter sprint performance in trained rugby union players. In this case, 97 male rugby union players were assigned to four groups: passive active stretch, active dynamic stretch, active static stretch, and static dynamic stretch. Participants performed a 10-minute jog and then two 20-meter sprints. They then completed their assigned stretching protocol and performed two more 20-meter sprints. The passive static stretch and the active static stretch groups had a significant increase in sprint time, whereas the active dynamic stretch group had a significant decrease in sprint time. The researchers concluded that static stretching as part of a warm-up may negatively effect 20-meter sprint performance, while active dynamic stretching may increase 20-meter sprint performance.
Fletcher and Jones (2004) suggested that the decrease in performance after stretching can be attributed to the same factors as those conjectured by Nelson et al. (2005). However, Fletcher and Jones differentiated between passive and active stretching. Neurologically, they proposed that passive stretching causes acute neural inhibition, decreasing neural drive to the muscle. Mechanically, they insinuated that passive stretching actually changes tendon structure, increasing the compliance of the tendon and therefore reducing force production and delaying muscle activation, supporting the findings of Kubo, Kanehisa, Kawakami, and Fukunaga (2001). Additionally, in accordance with Kokkonen et al. (1998), they stated that a stiffer musculotendinous unit will generate more force than a compliant one. Given that passive stretching increases the compliance of the musculotendinous unit, it can therefore be said that passive static stretching decreases performance that is reliant on force production.
However, Fletcher and Jones (2004) noted that in previous studies, prior to the concentric contraction, only a very slow eccentric contraction, or none at all, was employed. Sprinting requires the rapid, continuous change from eccentric to concentric contraction. Prior to this study, the effect of static stretching on sprint performance had not been explored. However, previous work on the effects of stretching on activities that employ the stretch-shortening cycle, such as drop jumps, indicates the effects stretching may have on sprinting (Young & Elliott, 2001). It appears that passive stretching primarily influences the eccentric phase of the cycle, reducing elastic return. As stated by Nelson et al. (2005), this reduction in retention of elastic energy is the result of increased compliance of the musculotendinous unit.
With regards to active stretching, Fletcher and Jones (2004) suggested that the detriment in performance could be the result of a reduction in muscle spindle sensitivity, caused by reduced sensitivity of the neural pathways after a prolonged isometric contraction. This occurs because as the agonist contracts, the antagonist relaxes, causing reciprocal inhibition (the decrease of excitatory impulses through the nervous system to the motor units). Therefore, in activities such as sprinting where muscle pairs are required to function together, the performance ability of one muscle in a functioning pair may be hampered by a reduction in nervous system stimuli.
Recently, the effect of static stretching on sprint performance has been further explored by Little and Williams (2006), who aimed to identify the effects of different warm-up protocols on high-speed motor capacities in elite soccer players, including acceleration and maximal velocity. Contrary to previous findings, static stretching was found to have no effect on sprint performance. |
8. What Does The Research Say? |
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The benefits of static stretching are commonly conjectured to include a decrease in injury risk and an increase in muscle performance. However, even though the research assessing the effects of static stretching is limited, results of published studies to date indicate that static stretching prior to activity not only doesn't achieve the desired effects, but can actually decrease performance when compared to a warm-up protocol that does not include static stretching. These findings are common across studies assessing the effect of static stretching on maximal strength performance of the muscle, explosive force production, and sprint performance. Therefore, an alternative to static stretching is required in order to ensure that pre-performance warm-up routines do not diminish the athlete's ability to perform to his or her maximum physical capabilities. |
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Boyle, P. M. (2004). The effect of static and dynamic stretching on muscle force production. Journal of Sport Sciences, 22, 273-274.
Cramer, J. T., Housh, T. J., Johnson, G. O., Miller, J. M., Coburn, J. W., & Beck T. W. (2004). Acute effects of static stretching on peak torque in women. Journal of Strength and Conditioning Research, 18, 236-241.
Cramer, J. T., Housh, T. J., Weir, J. P., Johnson, Coburn, J. W., & Beck T. W. (2005). The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography. European Journal of Applied Physiology , 93, 530-539.
Dadebo, B., White, J., & George, K. P. (2004). A survey of flexibility training protocols and hamstring strains in professional football clubs in England . British Journal of Sports Medicine, 38, 388-394.
Donatelle, R., J. (2003). Health: The basics (5 th edition) . San Francisco , CA : Benjamin Cummings.
Fletcher, I. M., & Jones, B. (2004). The effect of different warm-up stretch protocols on 20-meter sprint performance in trained rugby union players. Journal of Strength and Conditioning Research, 18, 885-888.
Herbert, R. D., & Gabriel, M. (2002). Effects of stretching before and after exercising on muscle soreness and risk of injury: Systematic review. British Medical Journal, 325, 468-470.
Kokkonen, J., Nelson, A. G., & Cornwell, A. (1998). Acute muscle stretching inhibits maximal strength performance. Research Quarterly for Exercise and Sport, 69, 411-415.
Kubo, K., Kanehisa, H., Kawakami, Y., & Fukunaga, T. (2001). Influence of static stretching on viscoelastic properties of human tendon structures in vivo. Journal of Applied Physiology, 90, 520-527.
Laur, D. J., Anderson, T., Geddes, G., Crandall, A., & Pincivero, D. M. (2003). The effects of acute stretching on hamstring muscle fatigue and perceived exertion. Journal of Sports Sciences, 21, 163-170.
Little, T., & Williams, A. G. (2006). Effects of differential stretching protocols during warm-ups on high-speed motor capacities in professional soccer players. Journal of Strength and Conditioning Research, 20, 203-207.
Magnusson, S. P., Simonsen, E. B., Aagaard, P., & Kjaer, M. (1996). Biomechanical responses to repeated stretches in human hamstring muscle in vivo. The American Journal of Sports Medicine, 24, 622-628.
Moeller, M., Ekstrand, J., Oberg, B., & Gillquist, J. (1985). Duration of static stretching effect on range of motion in lower extremities. Archives Journal of Sports Medicine, 22, 171-173.
Nelson, A. G., Driscoll, N. M., Landin, D. K., Young, M. A., & Schexnayder, I. C. (2005). Acute effects of passive muscle stretching on sprint performance. Journal of Sports Sciences, 23, 449454.
Pope, R. P., Herbert, R. D., Kirwan, J. D., & Graham, B. J. (2000). A randomized trial of preexercise stretching for prevention of lower-limb injury. Medicine and Science in Sports and Exercise, 32, 271-277 .
Rosenbaum, D., & Hennig, E. (1995). The influence of stretching and warm-up exrcises on Achilles tendon reflex activity. Journal of Sports Sciences, 13, 481-490.
Siatras, T., Papadopoulos, G., Mameletzi, D., Gerodimos, V., & Kellis, S. (2003). Static and dynamic acute stretching effect on gymnasts' speed in vaulting. Pediatric Exercise Science, 15, 383-391.
Thacker, S. B., Gilchrist, J., Stroup, D. F., & Kimsey, Jr., C. D. (2004). The impact of stretching on sports injury risk: A systematic review of the literature. Medicine and Science in Sports and Exercise, 36, 371-378.
Young, W., & Elliott, S. (2001). Acute effects of static stretching, proprioceptive neuromuscular facilitation stretching, and maximum voluntary contractions on explosive force production and jumping performance. Research Quarterly for Exercise and Sport, 72, 273-277.
Young, W. B., & Behm, D. G. (2003). Effects of running, static stretching and practice jumps on explosive force production and jumping performance. Journal of Sports Medicine and Physical Fitness, 43, 21-27. |
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